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Why are dosages for estrogen suppression drugs one-size-fits-all?
Breast Cancer | Last Active: Apr 1 10:56am | Replies (56)Comment receiving replies
The dosage for Letrozole was discussed here on another thread maybe a year or so back. Because of that discussion I asked my oncologist and he agreed to put me on a half dose. I will look for the research. In the meantime I found this research on Anastrazole. I'm providing the link, but I've also cut/pasted the most pertinent paragraph. The parenthesis content is my addition.
https://www.drugs.com/pro/anastrozole.html
(estradiol=estrogen)
Mean serum concentrations of estradiol were evaluated in multiple daily dosing trials with 0.5, 1, 3, 5, and 10 mg of Anastrozole tablets in postmenopausal women with advanced breast cancer. Clinically significant suppression of serum estradiol was seen with all doses. Doses of 1 mg and higher resulted in suppression of mean serum concentrations of estradiol to the lower limit of detection (3.7 pmol/L). The recommended daily dose, Anastrozole tablets 1 mg, reduced estradiol by approximately 70% within 24 hours and by approximately 80% after 14 days of daily dosing. Suppression of serum estradiol was maintained for up to 6 days after cessation of daily dosing with Anastrozole tablets 1 mg.
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Thanks for posting this info and link! I would really like to find the original article with the clinical data. I came across a 1996 article, very small groups, also about dosing and am wondering about the 'below level of detection' difference betw .5 and 1 mg of Arimidex, but which is mentioned that result found 24 hrs after last dose...so doesn't explicitly mention if that was also the case during the 14-day testing period....(study funded by Zeneca, btw)
Arimidex (ZD1033): a selective, potent inhibitor of aromatase in postmenopausal female volunteers
RA Yates', M Dowsett2, GV Fisher', A Selen3 and PJ Wyld4 'Zeneca Pharmaceuticals, Alderley Park, Macclesfield, Cheshire SKIO 4TG, UK; 2Royal Marsden Hospital, Fulham Road, London, SW3 6JJ, UK; 3Zeneca Pharmaceuticals, 1800 Concord Pike, Wilmington, USA; 4Inveresk Clinical Research Ltd, Riccarton, Edinburgh, UK.
Summary
Two multiple-dose studies were conducted in healthy post-menopausal female volunteers to investigate the pharmacokinetics and effects on endocrinology of Arimidex (ZD1033). Volunteers in the first trial were dosed with 3 mg of ZD1033 daily over 10 days to assess the effects on endocrinology of ZD1033 and establish the pharmacokinetic profile. In the second trial volunteers received 14 daily doses of either 0.5 or 1.0 mg of ZD1033 to assess the pharmacokinetics of ZD1033 and the effects of low doses of ZD1033 on serum oestradiol concentrations. Following multiple dosing a significant reduction in the concentration of serum oestradiol of approximately 80% of baseline was obtained with all three doses; no recovery in oestradiol was apparent for up to 144 h after the last dose. There was no overall difference in the level of oestradiol suppression between the 0.5 or 1.0 mg doses of ZD1033. However, comparison of the number of volunteers with oestradiol concentrations below the limits of detection of the assay, 24 h after the last dose of ZD1033, suggested that 1.0 mg was the minimal dose required for maximal suppression of oestradiol.